Bleaching composition



United States Patent Ofilice 3,345,303 Patented Oct. 3, 1967 3,345,303 BLEACHING COMPOSITION Hans G. Schmid, New Providence, and Gerald R. Ferrante, Metuchen, N.J., assignors to Shell Oil Company, New York, N.Y., a corporation of Delaware N Drawing. Filed Dec. 8, 1964, Ser. No. 416,895

4 Claims. (Cl. 252-186) ABSTRACT OF THE DISCLOSURE An improved process for bleaching cotton and like fabrics comprises applying to the fabric a solution consisting essentially of water, hydrogen peroxide and sodium citrate, and having a pH of from 6 to 9.

This invention relates to the bleaching of cotton and like cellulosic fabrics with hydrogen peroxide. It deals with an improved method for carrying out such bleaching and with novel solutions for use therein.

Cotton bleaching with hydrogen peroxide is carried out on a very large scale. In typical commercial practice, dilute aqueous hydrogen peroxide is used at a pH between about 10 and 11. Operation in this pH range has been conisdered necessary in order to obtain a relatively rapid bleaching rate while avoiding excessive fiber damage. For control of the pH in this alkaline range, sodium silicate has been the preferred butler because it is thought to reduce somewhat the amount of peroxide decomposition at high pH and to have some detergent and penetrating powers. However, under the best of circumstances, the bleaching has been slower than would be desirable and damage to the fibers has not been entirely avoided. Furthermore, the sodium silicate has the serious disadvantage of forming crusty deposits in the bleaching equipment. These cause rub marks on the fabric being bleached as the cloth is pulled through the machines during processing. Such marks make the goods unacceptable and are responsible for substantial financial losses in bleaching.

A great many proposals have been advanced from one time or another as to possible ways of avoiding the'dis advantages of peroxide bleaching of cotton in the presence of sodium silicate. While many of these have had some merit in certain respects, all have had offsetting disadvantages. The result has been that in spite of its many recognized deficiencies, bleaching with hydrogen peroxidecontaining sodium silicate has continued to be the most widely used method for cotton.

An object of the present invention is the provision of a new method of bleaching cotton and like cellulosic fibers with hydrogen peroxide without use of sodium silicate or similar components which cause deposits and lead to. damage of fabrics being bleached. It is a special object of the invention to provide a new bleaching process which not only avoids the undesirable features of prior peroxide bleaching in the presence of silicates, but also offers operating improvements of practical importance. More particularly, it is an object of the invention to provide a method by which bleaching of cellulosic fibers with hydrogen peroxide can be carried out more rapidly and with less damage to the fibers. Still other advantages of the invention will be apparent from the following description of some of its numerous methods of application.

In accordance with the invention, cellulosic fibers are bleached Without the use of sodium silicate by applying ;to the fibers a novel bleaching solution consisting essentially of an aqueous solution of hydrogen peroxide of pH 6 to 9 containing about 0.05 to about 1.5% weight hydrogen peroxide together with about 0.2 to about 2.0% weight of a water soluble salt of citric acid. i

The water-soluble citrate salt is preferably an alkali metal or ammonium salt, but alkaline earth metal citrates such as dibasic magnesium citrate or other citrate salts having sufiicient solubility to form the required solutions can be used successfully. Most preferably, citrate salts of cations of fixed valence are employed. Sodium and potassium citrates are particularly useful because of their availability at low cost. While citrate salt concentrations of about 0.2 to about 2.0% weight are generally useful, it is usually more advantageous to use concentrations between about 0.2 and 0.7% Weight.

The hydrogen peroxide concentration in the bleaching solution is most advantageously maintained between about 0.25% and 0.75% by weight. A pH between 7 and 9 is also preferred.

Any of the conventional methods of applying bleaching solutions to fibers can be employed in carrying out the bleaching with the new bleaching composition. A simple and effective procedure is to immerse the cellulosic fibers in the bleaching solution until the desired bleaching action has taken place. For bleaching fabric, the cloth can be pulled at a regulated rate through a bath of bleaching solution. For best results, the cloth should be desized and caustic scoured prior to bleaching. One suitable method of applying the bleaching compositions of the invention is the continuous bleaching range developed for the Union Underwear Company and described in Textile World, June 1954. In this method of bleaching, the cloth is first passed through a warm water wetting-out bath, then through squeeze rolls to remove excess liquor before being dropped into the bleaching solution. After a controlled period of time in the bleaching solution, the cloth is passed through squeeze rolls adjusted to maintain about saturation as the cloth passes to a J-box where the goods are kept at controlled temperature until completion of the bleach. The bleached cloth is drawn from the J-box through Washers and through a sour. With the sodium silicate-free peroxide bleaching solution of the invention, significantv improvements in quality of the bleached goods are achieved with improved efiiciency of operation. Other methods of applying the improved bleaching solution can also be successfully used. The fabric can, for instance, be first padded in open width with the new bleaching solution; and after leaving the padding mangle, the goods can be passed through a pot-eye to convert them to rope form before being heated and piled into a J-box where the bleaching is completed. The bleaching is followed by the usual washing treatment.

Instead of continuous methods of bleaching, one can use conventional batchwise methods. The bleaching can, for example, be carried out in the same kier employed for scouring the goods. The kier should be made of peroxide resistant material, for example, wood, or cement lined steel, or aluminum or the like. After the goods are scoured in the usual way, they are not withdrawn but the cloth is thoroughly washed, and then the bleaching solution is introduced and circulated. An advantageous method of circulating is by withdrawing solution from the top of the kier and pumping it into the well at the bottom from which it rises through the cloth charge. A heating coil in the well is useful tor temperature control.

Alternatively, a simple steep-bleach can be used in which the cotton is saturated with the hydrogen peroxide bleaching solution and then is kept at room or elevated temperature until the desired bleaching is achieved. Still other procedures are applicable, the invention not being limited with respect to the methods by which the new bleaching solutions are applied to the cellulosic material which is to be bleached. Multiple bleaching treatments, for example, can be applied with the same or difierent ment can be combined successfully with bleaching by e a G other bleaching agents, for instance, sodium hypochlorite bleaching, ch may be applied before or after he Amount of Dibasic Solution Average GE Filling Tensile bleaching with the new bleaching solutions. g gl g fi $3 PH gg f The temperature and tune of bleaching which will be most advantageous will depend upon the nature of the 5 (125 M 824 5 goods which is to be bleached. In bleaching cotton knit 0.5 as 84.7 9 goods in the previously described bleaching range, temperatures similar to those used with conventional silicatecontaining bleach solutions can be employed. Thus, tem- EXAMPLE III I peratures of about 100 F. to about 120 F. are suitable 10 Two samples of desized and scoured cotton print cloth for the bleach solution in the saturator while a higher temwere bleached in a continuous process J-box at 200-210 perature of about 190 to about 212 F. is preferably F. Each bleaching solution contained about 0.35% wt. maintained during the bleaching in the l-box which folhydrogen peroxide and 0.05% wt. Triton X-100 wetting lows the saturator. With other methods of application and agent. The cloth was saturated with liquid at a l/ 1 liquor other types of cotton goods, higher or lower temperatures to cloth weight ratio. Treatment time was 63 minutes. may be desirable. As a broad general rule, temperatures of about 100 F to about 260 F are useful tem- Anhydrous 42 B.-Sodium Filling Tensile Percent GE peratures between about 190 F. and about 220 F. are Citric Acid, Silicate, pH Strength Loss, Brightness usually more preferable. With temperatures in these gen- Percent Percent (Percent) er-al ranges, one can ordinarily obtain excellent bleaching 2O 89 6 with bleaching times of about 1 to about 300 minutes, ff? 33 g 1 more advantageously times of about 30 to about 60 minutes.

The following examples show in more detail some of T1915 example 9 the g l Y can be the suitable methods of using the new bleaching solutions obttfuned by the new citrate leac ing sys em in 021111- and demonstrate some of the numerous advantages which parison with the COIIVBHUOHQI'SI icate system at essen ia they provide ly the same degree of bleaching but with the advantage EXAMPLE I of avoiding crusty deposits on the equipment which necessitates routine clean-up time and frequently damage the DeSlZed and scoured Cotton Pflnt cloth l whlfih fabric. Silicate deposits in fabric and alkali media may had an average GE whiteness of 67.8% and a filling tensile impart harsh to the bleached f b i hi h i Strength 9 Were bleached y fi 1/1 avoided in the process of the invention. Also avoided is cloth-llquld Tatlo using y peroxlde of residual alkalinity in the fabric which is undesirable be- 0.l4 to 035% Wt. concentration containing1 VaIIOIIJJ cause it neutralizes catalysts used in resin finishing. amounts 0 sodium citrate formed in the so ution y adding citric acid and then neutralizing with sodium hy- EXAMPLE IV droxide to a pH in the range of 7.0 to about 9. In each Due to the lower pH at which the new solutions can be case the bleach solution also contained 0.05% wt. of successfully used, they have the advantage over conven- Triton X-100, an alkylated aryl polyether alcohol which tional bleaching bath solutions containing silicate that is a conventional wetting agent. The samples were steamed 40 they do not cause sensitive dyes to bleed into areas to be at 212 F. and the following results were obtained at bleached or undergo shade changes and become dull. This bleaching times of 35 and minutes: is shown by tests in which cotton terry-cloth containing Solution Make-Up Bleaching Average Filling Time pH GE Whiteness Tensile Loss,

Anhydrous H102 (min) (Percent) (Percent) Citric Acid (Percent Wt.)

(Percent Wt.)

0. o. 35 50 7. 0 87.0 11 0. 0. 35 50 7. 5 87. 3 9 0.13 0. i4 35 8.0 83.6 0. 2e 0. 21 35 s. 1 86. 2 13 0. 65 0.28 50 8.0 87.3 10 0. 65 0. 35 50 8. 0 87.0 11 0. 55 0. 35 50 8.8 87.9 10

These results show that the new solutions give excellent alakali-sensitive naphthol dyes of red, yellow, and black bleaching and low tensile losses under a variety of condistripes separated by unscoured white stripes were bleached tions and are fully equal tothe best obtainable with sodiwith citrate and silicate bleaching solutions. The bleaching um silicate where 1% silicate is required and a pH of 10.3 solutions included 0.35% wt. hydrogen peroxide and must be used to achieve equal whiteness. 65 0.05 wt. Triton X100 wetting agent. The bleaching solutions were applied at 1/1 liquor to cloth weight ratio XA PL I E M E I and the samples were steamed one hour at 212 F.

The effectiveness of ammonium citrate in place of the sodium citrate of Example I in the new bleaching solu- Appearance after Bleaching tions was shown by tests with the same desized and htgdggu s 421g dium H l 1 iica e, scoured cotton print cloth. The hydrogen peroxide s olu- Percentwt Percent wt p 0010, which Compare t1on had a concentration of 0.35% wt. and contained d lt 0.05 wt. Triton X-100 wetting agent. It was applied mp6 at a liquid to cloth weight ratio of 1/1 after which the cloth was steamed at 212 F. The treatment time was 60 "i'ff" 312 $2,? Ejjfifigfi minutes.

Some of the dye from the red stripe bled into the White stripe during the silicate bleach whereas no bleeding occurred during the citrate bleach. Because of the reduced loss of hydrogen peroxide during bleaching with the new solutions, less peroxide is required initially in the bleach formulation than when sodium silicate is used. There is consequently a saving in bleaching cost.

It Will thus be seen that the invention otters many advantages and is capable of considerable variation. While, as previously indicated, the new solutions consist essentially of the hydrogen peroxide and citrate salt in the specified proportions, this does not preclude the presence of small amounts of other components, such, for instance, as the Wetting agent employed in the illustrative tests, which do not change the results to any significant extent. Thus, the wetting agent mentioned is not essential and can be omitted. Trace amounts of conventional hydrogen peroxide stabilizers such as sodium stannate, etc., or of fiber-protecting agents or optical brighteners, or the like, are other optional components of the new bleaching solutions. Also instead of bleaching cellulosic fibers alone, as illustrated in the foregoing examples, one can bleach blends of cotton and synthetic fibers satisfactorily by the process of the invention. Good results have been obtained in bleaching polyester-cotton blends, for instance, with hydrogen peroxide solutions containing sodium citrate at pH 7 to 9. The invention is thus not restricted to the bleaching solutions which have been given by Way of illustration only, nor to the cotton fabrics given as examples of the cellulosic fibers which can be bleached by the new method. Also the invention is not limited by any theory proposed in explanation of the improved results which are obtained.

We claim as our invention:

1. A bleaching bath solution particularly adapted for cotton bleaching consisting essentially of an aqueous solution of hydrogen peroxide of pH 6 to 9 containing about 0.05 to about 1.5% Weight hydrogen peroxide together With about 0.2 to about 2.0% weight of a sodium salt of citric acid.

2. A bleaching bath solution in accordance with claim 1 wherein the pH is between 7 and 9 and the salt is a citrate having a cation of invariant valence.

3. A bleaching solution in accordance with claim 2 wherein the salt is sodium citrate which is present in a concentration of 0.2 to 0.7% by Weight of the solution.

4. A process for bleaching cellulosic fibers which comprises applying to the fabric an aqueous solution having a pH in the range of 6 to 9 and consisting essentially of Water, about 0.25 to about 0.75% weight hydrogen peroxide, and about 0.2 to about 0.5% Weight of sodium citrate.

References Cited UNITED STATES PATENTS 3,259,584 7/1966 Moyer 252-186 LEON D. ROSDOL, Primary Examiner. M. WEINBLATI, Assistant Examiner. 

1. A BLEACHING BATH SOLUTION PARTICULARLY ADAPTED FOR COTTON BLEACHING CONSISTING ESSENTIALLY OF AN AQUEOUS SOLUTION OF HYDROGEN PEROXIDE OF PH 6 TO 9 CONTAINING ABOUT 0.05 TO ABOUT 1.5% WEIGHT HYDROGEN PEROXIDE TOGETHER WITH ABOUT 0.2 TO ABOUT 2.0% WEIGHT OF A SODIUM SALT OF CITRIC ACID. 